Interhemispheric transmission time in an auditory two-choice reaction task.

An unimanual auditory choice reaction task was performed by 16 right-handed male subjects. Upon release of a central ready button subjects pressed a target button on their right or left side depending on the ear in which they heard a tone. A significant 'Ear' x 'Hand' interaction effect appeared on both reaction time (RT) and the first component of movement (MT1), showing that uncrossed conditions give rise to faster responses than crossed conditions. Interhemispheric transmission time (IHTT) was estimated from the difference of response latency in the two types of conditions. No asymmetry in the speed of information transfer between the hemispheres was found. IHTT was 16 ms in the case of RT, which supported previous research with visual reaction tasks, and IHTT for MT1 was 13 ms, which has not been reported before.